In an electrohydraulic unit of this general type referred to hereinabove WO94/08830A, the axes of the accommodating bores for the control valves lie in two parallel planes and have equal dimensions. This has detrimental effects on the overall size of the housing.
An object of the present invention is to reduce the mounting space required for the housing in a unit of the type mentioned hereinabove without suffering from disadvantages in terms of function and rendering the manufacture more expensive.
According to the present invention, this object is achieved because the control valves, which are connected to the slave cylinders of one vehicle axle that have a volume requirement lower than the volume requirement of the slave cylinders of the other vehicle axle, and the accommodating bores of these control valves have a smaller diameter and are arranged offset from the middle of the row in the direction of the third housing surface.
The present invention is based on the recognition that the volume requirement of the slave cylinders on the rear axle of the vehicle, which is low in most vehicle brake systems, permits greatly reducing the size of the control valves for controlling the braking pressure of the slave cylinders without impairing the function, and that the reduction in size of the control valves can favorably be used to reduce the mounting space required for the housing of the electrohydraulic unit by moving the accommodating bores for the control valves closer together and by arranging them offset to one housing side. The space obtained by this measure permits moving the bores of the pressure accumulators closer to the middle of the housing so that the overall length of the housing in the axial direction of the bores can be shortened, yet the accumulator volume is maintained. When the accommodating bores with equal diameter are disposed in both bore rows side by side, the housing may be reduced in size in the direction of the bore rows in addition. The reduced dimensions of the housing and the reduced efforts in machining the smaller accommodating bores and the smaller valve designs additionally achieve a reduction of manufacturing costs.
According to the present invention, a supplementary measure of diminishing the housing dimensions may involve that the bores of the damping chambers are configured as stepped bores whose small-diameter step projects over the bottom of the adjacent accommodating bores. Further, it may be provided that the axes of the two steps of the stepped bores are arranged in parallel to one another so that the position of the small step is to a certain degree independent of the position of the large step.
The design of the electrohydraulic unit according to the present invention further renders it possible to arrange an additional arcuate row of large-size accommodating bores for accommodating further control valves between the bores of the pressure accumulators and the damping chambers and the accommodating bores adjacent thereto by only extending the housing in one direction, i.e., in the direction of the bore axes of the pressure accumulators. The further control valves are used for an automatic activation of the brake system, for example, for traction slip or driving stability control. The arrangement of the additional valve row offers the advantage that the bore pattern for the passages for connecting the accommodating bores, connecting bores and pressure accumulator and damping chamber bores in a housing without additional valve row and a housing with an additional valve row may be identical except for minor modifications, and that only a small number of additional passage bores are required for connecting the additional valve row. This facilitates chip-cutting machining operations, and the number of tools necessary remains small. Also, the assembly of the structural elements is simple because identical structural elements are always seated in the same location.